Security alarm systems often use magnetic switches attached to doors and windows for detecting unauthorized openings. One type of magnetic switch utilized is a reed switch. However, these switches are subject to unauthorized manipulation through use of, for example, an external magnet. Specifically, a compact high energy magnet may be positioned in proximity to the reed switch, which will then be operated (to either open or close depending on the control scheme). Once accomplished, an intruder may open the door or window without triggering the alarm system.
A number of magnetic switches have been proposed in the past to overcome the inherent limitation and serious deficiencies of reed switches including, U.S. Pat. Nos. 5,997,873; 5,530,428; 5,332,992; 5,673,021; 5,880,659; and 6,506,987. These switches typically include a pair of spaced apart switch elements with a shiftable body (e.g., a spherical ball) movable between a first position where the ball is in simultaneous contact with both switch elements and a second position out of simultaneous contact with the switch elements. An alarm circuit may be electrically coupled to the switch elements so as to detect movement of the body. However, these switches may still be manipulated by an externally applied magnetic force.
Other systems have been presented that also offer limited protection from external magnetic manipulation including, U.S. Pat. Nos. 6,506,987; 6,603,378; and 6,803,845. While the switch arrangements in these patents represent an improvement in the field, these switch arrangements suffer from some inherent problems. For example, while offering a degree of security against external magnetic fields in one plane, these switches may still be defeated by introducing an external magnetic force in one of several or in multiple planes. Another problem presented by these switches is that they are prone to misalignment, causing problems with accurate functioning of the system. In addition, these switches may be highly sensitive to the material to which they are mounted. For example, if these switches are mounted to a steel base, a portion of the magnetic field strength may be drawn away negatively affecting system performance.
Another system is disclosed in U.S. Pat. No. 5,877,664 entitled Magnetic Proximity Switch System. This system teaches use of an armature member that may be shifted to various positions to electrically open or close various contacts depending upon the position of a magnet. For example, when a first magnet is in a first position, the armature member resides in a first position. But when the first magnet is moved to a second position, the armature member may then be drawn to a second position by a second magnet. The '664 patent further teaches that at least two switch pole pieces may be used in conjunction with each other to provide off switch axis actuation or actuation though surfaces not normal to the axis of the switch. However, a problem with the '664 patent is that, the device cannot tolerate fields off axis leading to operational problems. Without a pole piece, flux leakage could result in off axis leakage disadvantageously affecting the performance of the switch. To compensate for this, the '664 patent provides at least two pole pieces to redirect the magnetic flux. This disadvantageously requires increased space and hardware to accomplish.
Another problem with the '664 patent is that there is no way to control the amount of magnetic flux that is applied to a switch. Rather, the '664 patent is designed merely to maximize magnetic flux to the device when transmitted off axis. Accordingly, there is no way to generate or maintain a particular field strength at the switch.
Still another problem with the '664 patent is that there is no way to channel magnetic flux applied to the pole piece in different directions to, for example, multiple switches. Rather, to change the direction of the magnetic field, the '664 patent teaches that at least two pole pieces are required to accomplish this. In fact, only one cross-sectional area provides the active surface for the pole piece. Again this leads to increased space requirements, additional materials and expense.
Finally, due to the configuration of system taught in the '664 patent with the at least two pole pieces, the system is prone to misalignment problems. While the at least two pole pieces are used to channel off axis magnetic flux, they do not address the problems created caused by misalignment and must be positioned relatively close to each other to function properly.
Misalignment can cause magnetic systems to malfunction. For example, the magnetic field that transfers from one piece to another across an operational air gap (e.g. the door jam) must be kept in relative close proximity to each other. The various pieces of the magnetic system may be installed correctly, however, over time the door may sag thereby increasing the distance and causing misalignment of the various pieces, which may adversely affect the performance of the system.
What is desired then, is a system and method that will provide an improved magnetic switching device that is essentially undefeatable by application of an externally applied magnetic field.
It is further desired to provide a system and method that provides an improved magnetic switching device that may not be defeated with the application of an external magnetic field in one of several or multiple planes.
It is still further desired to provide a system and method that provides an improved magnetic switching device that reduces sensitivity to system misalignment.
It is yet further desired to provide a system and method that provides an improved magnetic switching device that is relatively insensitive to the material to which they are mounted.
It is also desired to provide a system and method for controlling the magnetic flux intensity that may be applied to a switch component.
It is still further desired to provide a system and method that gathers and channels magnetic flux to several or in multiple directions for application to various switches.
It is yet further desired to provide a system and method that may be used to increase the total amount of magnetic flux applied to a switch component.
It is still further desired to provide a system and method for variably adjusting the positions of the various pieces used in a magnetic switching arrangement to compensate for movement of the members upon which the pieces are affixed.